Artifact Volume Research Articles

Improving Structure Delineation for Radiation Therapy Planning Using Dual-Energy CT.

PurposeWe present the advantages of using dual-energy CT (DECT) for radiation therapy (RT) planning based on our clinical experience.MethodsDECT data acquired for 20 representative patients of different tumor sites and/or clinical situations with dual-source simultaneous scanning (Drive, Siemens) and single-source sequential scanning (Definition, Siemens) using 80 and 140-kVp X-ray beams were analyzed. The data were used to derive iodine maps, fat maps, and mono-energetic images (MEIs) from 40 to 190 keV to exploit the energy dependence of X-ray attenuation. The advantages of using these DECT-derived images for RT planning were investigated.ResultsWhen comparing 40 keV MEIs to conventional 120-kVp CT, soft tissue contrast between the duodenum and pancreatic head was enhanced by a factor of 2.8. For a cholangiocarcinoma patient, contrast between tumor and surrounding tissue was increased by 96 HU and contrast-to-noise ratio was increased by up to 60% for 40 keV MEIs compared to conventional CT. Simultaneous dual-source DECT also preserved spatial resolution in comparison to sequential DECT as evidenced by the identification of vasculature in a pancreas patient. Volume of artifacts for five patients with titanium implants was reduced by over 95% for 190 keV MEIs compared to 120-kVp CT images. A 367-cm3 region of photon starvation was identified by low CT numbers in the soft tissue of a mantle patient in a conventional CT scan but was eliminated in a 190 keV MEI. Fat maps enhanced image contrast as demonstrated by a meningioma patient.ConclusionThe use of DECT for RT simulation offers clinically meaningful advantages through improved simulation workflow and enhanced structure delineation for RT planning.

Evaluation of magnetic resonance imaging artifacts caused by fixed orthodontic CAD/CAM retainers\u2014an in vitro study

ObjectivesMagnetic resonance imaging (MRI) image quality can be severely impaired by artifacts caused by fixed orthodontic retainers. In clinical practice, there is a trend towards using computer-aided design/computer-aided manufacturing (CAD/CAM) retainers. This study aimed to quantify MRI artifacts produced by these novel CAD/CAM retainers.Material and methodsThree CAD/CAM retainers and a stainless-steel retainer (“Twistflex”; clinical reference standard) were scanned in vitro at 3-T MRI using a high-resolution 3D sequence. The artifact diameters and three-dimensional artifact volumes (AV) were determined for all mandibular (AVmand) and maxillary (AVmax) retainers. Moreover, the corresponding ratio of artifact volume to retainer volume (AV/RVmand, AV/RVmax) was calculated.ResultsTwistflex caused large artifact volumes (AVmand: 13530 mm3; AVmax: 15642 mm3; AV/RVmand: 2602; AV/RVmax: 2235). By contrast, artifact volumes for CAD/CAM retainers were substantially smaller: whereas artifact volumes for cobalt–chromium retainers were moderate (381 mm3; 394 mm3; 39; 31), grade-5 titanium (110 mm3; 126 mm3; 12; 12) and nickel–titanium (54 mm3; 78 mm3; 12; 14) both produced very small artifact volumes.ConclusionAll CAD/CAM retainers caused substantially smaller volumes of MRI artifacts compared to Twistflex. Grade-5 titanium and nickel–titanium CAD/CAM retainers showed the smallest artifact volumes.Clinical relevanceCAD/CAM retainers made from titanium or nickel–titanium may not relevantly impair image quality in head/neck and dental MRI. Artifacts caused by cobalt–chromium CAD/CAM retainers may mask nearby dental/periodontal structures. In contrast, the large artifacts caused by Twistflex are likely to severely impair diagnosis of oral and adjacent pathologies.

Intelligent Motion Correction Significantly Impacts The Volumes Of Calcium Blooming Artifacts For Coronary Computed Tomography Angiography (CCTA)

Introduction: Calcification in the coronary arteries can be overestimated due to calcium blooming that alters the size and shape of calcified plaques. Blooming which is caused by motion, beam hardening, and partial volume artifacts, continues to be a challenge in CCTA and can lead to higher false positive rates for obstructive CAD. While results of a prototype de-blooming algorithm (GE Healthcare) have been previously published, the addition of a second-generation, whole-heart motion correction algorithm (SnapShot Freeze 2, “SSF2”, GE Healthcare) and its benefits to the overall de-blooming solution has yet to be investigated. The purpose of this study is to assess the combined effects of SSF2 intelligent motion correction and the de-blooming algorithm on the calcified plaque burden present in CCTA.

Influence of magnetic susceptibility and volume on MRI artifacts produced by low magnetic susceptibility Zr-14Nb alloy and dental alloys.

The artifact volume generated in magnetic resonance (MR) images was quantitatively evaluated to investigate how artifact behavior correlates to the magnetic susceptibility and volume of an implanted metal device. For this, a new low-magnetic-susceptibility Zr-14Nb alloy was compared with two conventional dental alloys, Ti-6Al-7Nb alloy and Co-Cr-Mo alloy, using spherical specimens of each alloy prepared with four different diameters. Then, MR images were recorded under fast spin echo and gradient echo conditions, from which the artifact volume was measured. The artifact volume decreased with the magnetic susceptibility, volume, and mass of the specimens, and significant linear correlations were observed. The artifact volume can be estimated by the equations presented here; nevertheless, further studies are necessary to interpret the influence of some important factors (e.g., imaging conditions, shape, and orientation) to predict the artifact volume more precisely.

Metal artifact reduction of orthopedics metal artifact reduction algorithm in total hip and knee arthroplasty.

The purpose of this study was to investigate metal artifact reduction effect of orthopedics metal artifact reduction (O-Mar) algorithm in computer tomography (CT) image of patients who have undergone total hip arthroplasty (THA) or total knee arthroplasty (TKA).35 cases of patients who underwent TKA or THA have been recruited in this study. CT image of hip or knee joint was obtained with Philips 256-row CT scanner. Tube voltages of 120 and 140 kilovolt peak (KVP) were set. Afterwards, CT image was reconstructed by O-Mar algorithm to reduce metal artifact. Grade of image quality and severity of metal artifact would be taken into qualitative evaluation. While, quantitative evaluation mainly included measurement of metal artifact volume and 2D measurement of average CT value in region of interest (ROI). The visibility of interface between bone–prostheses was also estimated.Result of qualitative analysis indicated that score of CT quality was improved and grade of metal artifact was decreased significantly with O-Mar. Quantitative analysis illustrated that volume of beam-hardening (B-H) metal artifact decreased remarkably after reconstruction of O-Mar (P < .001). In addition, O-Mar algorithm reduced 83.3% to 83.7% volume of photon-starvation (P-S) metal artifact. As for result of 2D measurement, CT value in ROI was closer to standard value in O-Mar group CT image (P < .001). Meanwhile, error of CT value also decreased significantly after reconstruction of O-Mar algorithm. Visibility rate of bone–prosthesis interface improved from 34.3% (Non-O-Mar) to 66.7% (O-Mar).O-Mar algorithm could significantly reduce metal artifact in CT image of THA and TKA in both 2D and three-dimensional (3D) level. Therefore, better image quality and visibility of bone–prostheses interface could be presented. In this study, O-Mar was proved as an efficient metal artifact reduction method in CT image of THA and TKA.

Location and Volume of MRI Artifacts in Patients With Implanted Sphenopalatine Ganglion Neurostimulators for Treatment of Chronic Cluster Headache

Sphenopalatine ganglion stimulation (SPG-S) is an invasive form of neuromodulation by which a neurostimulator is implanted into the pterygopalatine fossa to treat refractory chronic cluster headache. The implant is MRI conditional, up to 3 T, however there is no clinical data on the shape, size, and location of the artifact produced by the implant. Records of patients with SPG-S were analyzed for postoperative cranial MRI scans. MRI and intraoperative CT scans for visualization of the implant were fused and volumetry was performed for both the implant and the MRI artifact in different MRI sequences. In total, n = 3 patients with postoperative MRI scans were identified. The mean CT artifact volume was 0.73 cm3 (±0.15 cm3 ). MRI artifact volume differed between sequences (range: 25.2-220.7 cm3 ). The intracranial space was largely unaffected besides the pole of the ipsilateral temporal lobe and the basal frontal gyrus. MRI artifacts affected the extracranial space (orbit, maxillary and ethmoid sinuses, and parts of the parotid gland). No adverse events occurred during or after MRI scans. Cranial MRI scans with SPG-S implants were safely performed in three patients following the manufacturer's MRI conditions. MRI artifacts were mostly located in the extracranial space. Brain MRI imaging is largely unaffected. The authors declare no potential conflicts of interest with respect to research, authorship, and/or publication of this article.

Quantification of metal-induced susceptibility artifacts associated with ultrahigh-field magnetic resonance imaging of spinal implants.

Reports on spinal‐implant metallic artifacts in 7‐T magnetic resonance imaging (MRI) are lacking. Thus, we investigated the magnitude of metal artifacts derived from spinal implants in 7‐T MRI and analyzed the differences obtained with spinal rods manufactured from pure titanium, titanium alloy, and cobalt‐chrome (5.5‐mm and 6.0‐mm diameters and 50‐mm length). Following the American Society for Testing and Materials guidelines, we measured the artifact size and artifact volume ratio of each rod during image acquisition using 7‐T MRI scanners with three‐dimensional (3D) T1‐weighted and 3D T2* spoiled gradient echo (GRE), 3D T2‐weighted fast spin echo, zero echo time (ZTE), and diffusion‐weighted imaging sequences. Pure titanium and titanium alloy rods yielded significantly smaller artifacts than did cobalt‐chrome rods, with no significant difference between pure titanium and titanium alloy rods. The artifact sizes of the 5.5‐mm and 6.0‐mm diameter rods were similar. The artifact magnitude increased in the following sequence order: ZTE, 3D T2 fast spin echo, 3D T1 spoiled GRE, 3D T2* spoiled GRE, and diffusion‐weighted imaging. Artifacts obtained using the spin echo method were smaller than those obtained with the GRE method. Because the echo time in ZTE is extremely short, the occurrence of artifacts because of image distortion and signal loss caused by differences in magnetic susceptibility is minimal, resulting in the smallest artifacts. ZTE can be a clinically useful method for the postoperative evaluation of patients after instrumentation surgery, even with 7‐T MRI.

Quantitative evaluation of artefact reduction from metallic dental materials in short tau inversion recovery imaging: efficacy of syngo WARP at 3.0 tesla.

To evaluate the effects of syngo WARP on reducing metal artefacts from dental materials. Short tau inversion recovery (STIR) with syngo WARP [a dedicated metal artefact reduction sequence in combination with view-angle-tilting (VAT)] was performed using phantoms of three dental alloys: cobalt-chromium (Co-Cr), nickel-chromium (Ni-Cr), and titanium (Ti). Artefact volumes and reduction ratios of black, white and overall artefacts in the standard STIR and syngo WARP images with several different parameter settings were quantified according to standards of the American Society for Testing and Materials F2119-07. In all sequences, the artefact volumes and reduction ratios were compared. The modulation transfer function (MTF) and contrast-to-noise ratio (CNR) were also measured for evaluation of image quality. In standard STIR, the overall artefact volume of Co-Cr was markedly larger than those of Ni-Cr and Ti. All types of artefacts tended to be reduced with increasing receiver bandwidth (rBW) and VAT. The effect of artefact reduction tended to be more obvious in the axial plane than in the sagittal plane. Compared with standard STIR, syngo WARP with a matrix of 384 × 384, receiver bandwidth of 620 Hz/pixel, and VAT of 100 % in the axial plane obtained reduction effects of 30 % (white artefacts), 45 % (black artefacts), and 38 % (overall artefacts) although MTF and CNR decreased by 30 and 22 % compared with those of standard STIR, respectively. syngo WARP for STIR can effectively reduce metal artefacts from dental materials.

Artifacts in cranial MRI caused by extracranial foreign bodies and analysis of these foreign bodies.

Purpose:The purpose of our study was to conduct a chemical analysis of extracranial foreign bodies (FBs) causing artifacts in cranial magnetic resonance imaging (MRI) and to investigate the association between chemical composition, magnetic susceptibility, and artifact size.Materials and Methods:A total of 12 patients were included in the study. The FBs responsible for the artifacts were visualized using cranial computed tomography (CT). Artifact-causing FBs were removed from the scalps of 10 patients and analyzed using scanning electron microscope with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction spectroscopy (X-RD), and Fourier-transform infrared spectroscopy (FT-IR). The magnetic susceptibility of the samples was determined using the reference standard material MnCl2.6H2O. The volume of the MRI artifacts was measured in cubic centimeters (cm3).Results:EDS results demonstrated that the mean Fe ratio was 5.82% in the stone samples and 0.08% in the glass samples. Although no phase peaks were detected in the X-RD spectra of the glass samples, peaks of Fe2O3, Al2Ca (SiO4) were detected in the X-RD spectra of the stone samples. The FT-IR spectra revealed metal oxide peaks corresponding to Fe, Al, in the stone samples and peaks confirming Al2SiO5 and Na2SiO3 structures in the glass samples. The mean volumes of the MRI artifacts produced by the stone and glass samples were 5.9 cm3 and 2.5 cm3, respectively.Conclusions:Artifacts caused by extracranial FBs containing metal/metal oxide components are directly associated with their chemical composition and the artifact size are also related to element composition and magnetic susceptibility.

Multicenter Volumetric Assessment of Artifactual Hypoperfusion Patterns using Automated CT Perfusion Imaging.

Automated computed tomography perfusion (CTP) is recommended to inform selection of stroke patients for thrombectomy >6 hours from last known normal (LKN). However, artifacts on automated perfusion output may overestimate the tissue at risk leading to misclassification of thrombectomy eligibility in some patients. We conducted a retrospective multisite study of consecutive patients with anterior large vessel occlusion (LVO) undergoing CTP (6/2017-12/2017). The primary outcome was the RAPID automated Tmax >6 seconds volume that was discordant with clinical symptoms and vessel imaging, manually assessed by two independent readers. The discordant penumbral volume was compared to the automated output and corrected mismatch ratios were generated. Of 410 consecutive patients who underwent CTP for suspected stroke, 60 (15%) had acute anterior circulation LVO. Of these, 26 (43%) had Tmax > 6 seconds abnormalities discordant with clinical symptoms and vessel imaging. There was strong interrater agreement on artifact volume (r2 = 0.927). Among patients with discordant Tmax imaging, the median artifactual volume was 12cc (IQR 3-21cc), accounting for a median of 8% of the automated Tmax > 6 seconds volume (IQR 3-16%, range 1-64%). Recalculation of the Tmax > 6 seconds volume resulted in 1 patient being reclassified as having an "unfavorable" mismatch ratio (2.04-1.40). Nearly half of patients had evidence of artifactual penumbral imaging on automated CTP, which rarely lead to misclassification of thrombectomy eligibility. Although artifactual findings are reliably identified by trained raters, our results emphasize the need to evaluate CTP results with knowledge of the patient's clinical symptoms and vascular imaging.

Three-dimensional quantification of magnetic resonance imaging artifacts associated with shape factors.

Differences in the volumes of artifacts caused by variously shaped titanium objects on magnetic resonance imaging (MRI) were evaluated. Spherical-, square cubic-, and regular tetrahedron-shaped isotropic, and elongated spherical-, elongated cubic-, and elongated tetrahedron-shaped anisotropic objects, with identical volumes, were prepared. Samples were placed on a nickel-doped agarose gel phantom and covered with nickel-nitrate hexahydrate solution. Three-Tesla MR images were obtained using turbo spin echo and gradient echo sequences. Areas with ±30% of the signal intensity of the standard background value were considered artifacts. Sample volumes were deducted from these volumes to calculate the total artifact volumes. Isotropic samples had similar artifact volumes. For anisotropic samples, the artifact volume increased in proportion with the normalized projection area. MRI artifact size can be reduced by high anisotropic designs, and by positioning the long axis of the metal device as parallel as possible to the magnetic field axis.

Metal Artifact Reduction in Cardiovascular MRI for Accurate Myocardial Scar Assessment in Patients With Cardiac Implantable Electronic Devices.

OBJECTIVE. An important application of late gadolinium enhancement (LGE) cardiac MRI is accurate assessment of myocardial scar before ablation. However, this is often limited in patients with cardiac implantable electronic devices (CIEDs) because of metal device-induced artifacts. The purpose of this study was to determine whether a modified wideband inversion recovery (IR) LGE MRI technique decreases artifact volume to allow the assessment of myocardial scar. SUBJECTS AND METHODS. Fifty patients (17 women and 33 men; mean age ± SD, 61 ± 12 years; mean ejection fraction ± SD, 35.9% ± 13.3%) with CIEDs underwent cardiac MRI using conventional and modified wideband IR LGE techniques before ablation. The volume of device-induced artifact was quantified and stratified by tertiles on mild, moderate, and severe. Ordinal logistic regression analysis assessed the association between artifact volume on conventional and wideband images adjusted for patients' demographics. RESULTS. Conventional LGE MRI resulted in device-induced hyperintense artifacts that obscured ventricular segments in 32 of 50 (64%) cases. Wideband LGE MRI significantly reduced severe artifact volume (p < 0.0001) and completely resolved all mild and most moderate artifacts. Overall, wideband techniques resulted in a 56% reduction in total artifact volume for the cohort (p < 0.0001). The wideband LGE MRI sequence minimized artifacts in the most commonly obscured segments on the conventional LGE MRI sequence, with persistent artifacts in seven, eight, and four of 32 cases at the basal anterior, midventricular anterior, and midventricular anteroseptal segments, respectively. CONCLUSION. The modified wideband IR technique completely resolves mild and moderate device-induced hyperintense artifacts and significantly reduces the volume of severe artifact to allow accurate identification of myocardial scar in patients with CIEDs before ablation.

The Newest Fixation Methods in Archaeology

The absolute and comprehensive research fixation is the main task of archaeology. One of the new methods is photogrammetry, which is rapidly gaining popularity in the world, because it does not require much time and labor involvement. Scaled 3D-models and orthophotomaps of monuments, buildings, objects and artifacts can be created by using photogrammetry technology.Any kinds of metrological measurements and researches in field and cameral archaeology are carried out with the help of computer programs. To be listed: post-expeditionary fixation and correction of plans and stratigraphies, color correction and orthophotomaps filtering, work with drawings during an expedition, measurements of necessary parameters and volumes of objects and artifacts, creating models for visualization, creating an interactive database, etc. Photogrammetry and 3D-modeling should become an integral methodological part of any archaeological research in the near future

Abstract WP129: Development of Cerebral Aneurysm Clips to Minimize Susceptibility Artifact by Magnetic Resonance Image

Objective: Surgical clipping is a major treatment modality in treating cerebral aneurysms. However, in magnetic resonance (MR) imaging, susceptibility artifact due to metal clips impedes postoperative assessments of clipped aneurysms, parent arteries, and adjacent parenchyma. Our goal was to develop an MR-compatible aneurysm clip. Methods: To reconcile mechanical/biologic properties with MR demands, we fabricated a prototypic clip (ZC: straight, 9-mm long), made of zirconia (body) and polyurethane (spring). Mechanical properties, closing forces, open-blade width, and artifact volumes (in vitro and in vivo) by 3T MR imaging of ZC and currently available metal clips (Yasargil [YC: curved, 8.3-mm long] and Sugita [SC: straight, 10-mm long]) were compared, using a canine venous pouch aneurysm model for in vivo study. Results: Respective closing force (N) values, measured at 1-mm and 8-mm distances from blade tip, were 2.09 and 3.77 in YC, 1.85 and 3.04 in SC, and 2.05 and 4.60 in ZC. Maximum open-blade widths (mm) were 6.8, 9.0, and 3.0 in YC, SC, and ZC, respectively. In vitro artifact volumes of YC and ZC were 26.0- and 1.9-fold greater than corresponding actual volumes. In vivo artifact volumes of YC, SC, and ZC were 21.4-, 29.4-, and 2.6-fold greater than actual volumes. Conclusion: Compared with two clips in current use, our prototypic clip showed the least susceptibility artifact, with satisfactory closing forces. However, its narrow open-blade width was a weak point. Further experimentation is needed for design refinements and durability testing before human application is feasible.

Carbon monofilament electrodes for unit recording and functional MRI in same subjects

Extracellular electrophysiology and functional MRI are complementary techniques that provide information about cellular and network-level neural activity, respectively. However, electrodes for electrophysiology are typically made from metals, which cause significant susceptibility artifacts on MR images. Previous work has demonstrated that insulated carbon fiber bundle electrodes reduce the volume of magnetic susceptibility artifacts and can be used to record local field potentials (LFP), but the relatively large diameter of the probes make them unsuitable for multi- and single-unit recordings. Although single carbon fiber electrodes have recently been used to record single-unit activity, these probes require modifications in order to aid insertion and the use of these probes in fMRI has yet to be validated. Therefore, there is a need for a single-carbon fiber electrode design that (1) minimizes the volume of the susceptibility artifact, (2) can record from a wide frequency band that includes LFP and multi- and single-unit recording, and (3) is practical to insert without additional modifications. Here, we demonstrate that carbon-fiber electrodes made from single carbon monofilaments (35 μm in diameter) meet all of these criteria. Carbon monofilament electrodes modified with the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) have lower impedances and higher signal-to-noise ratio recordings than platinum-iridium electrodes, a current gold standard for chronic single-unit recording. Furthermore, these probes distort a significantly smaller volume of voxels compared to tungsten and platinum-iridium electrodes in agarose phantom and in vivo MR images, leading to higher contrast-to-noise ratio in regions proximal to the electrode implantation site during fMRI. Collectively, this work establishes that carbon monofilaments are a practical choice for combined electrophysiology-fMRI experiments.

Effects of Cold Swaging on Mechanical Properties and Magnetic Susceptibility of the Zr–1Mo Alloy

Zr alloy is expected to decrease the artifact volume of magnetic resonance imaging (MRI) due to its relatively small magnetic susceptibility. To improve the mechanical properties of a Zr–1mass%Mo alloy that yielded a reduced artifact volume during MRI, the alloy was melted, hot-forged, and cold-swaged with area reduction ratios of 30%, 50%, 60%, 70%, and 84%. The effects of cold swaging on the microstructure, mechanical properties, and magnetic susceptibility of the alloy were investigated. Before cold swaging, the microstructure consisted of laminated and layered α- and β-phases; however, after cold swaging, the α- and β-phases were bent and distorted, and the α-phase became oriented along the {10 1¯ 0} plane. The ultimate tensile strength and elongation to fracture of the Zr–1Mo alloy after cold swaging with an 84% area reduction were 1001 MPa and 10.7%, respectively. The alloy only experienced work-hardening when subjected to large deformations. On the other hand, the change in magnetic susceptibility with cold-swaging was small, from 13.85 × 10−9 to 14.87 × 10−9 m3·kg−1. Thus, a good balance of mechanical properties and low magnetic susceptibility in the Zr–1Mo alloy was obtained by cold swaging. Therefore, this alloy is suitable for utilization in medical devices and is expected to decrease the artifact volume.

MSVAT-SPACE-STIR and SEMAC-STIR for Reduction of Metallic Artifacts in 3T Head and Neck MRI.

The incidence of metallic dental restorations and implants is increasing, and head and neck MR imaging is becoming challenging regarding artifacts. Our aim was to evaluate whether multiple-slab acquisition with view angle tilting gradient based on a sampling perfection with application-optimized contrasts by using different flip angle evolution (MSVAT-SPACE)-STIR and slice-encoding for metal artifact correction (SEMAC)-STIR are beneficial regarding artifact suppression compared with the SPACE-STIR and TSE-STIR in vitro and in vivo. At 3T, 3D artifacts of 2 dental implants, supporting different single crowns, were evaluated. Image quality was evaluated quantitatively (normalized signal-to-noise ratio) and qualitatively (2 reads by 2 blinded radiologists). Feasibility was tested in vivo in 5 volunteers and 5 patients, respectively. Maximum achievable resolution and the normalized signal-to-noise ratio of MSVAT-SPACE-STIR were higher compared with SEMAC-STIR. Performance in terms of artifact correction was dependent on the material composition. For highly paramagnetic materials, SEMAC-STIR was superior to MSVAT-SPACE-STIR (27.8% smaller artifact volume) and TSE-STIR (93.2% less slice distortion). However, MSVAT-SPACE-STIR reduced the artifact size compared with SPACE-STIR by 71.5%. For low-paramagnetic materials, MSVAT-SPACE-STIR performed as well as SEMAC-STIR. Furthermore, MSVAT-SPACE-STIR decreased artifact volume by 69.5% compared with SPACE-STIR. The image quality of all sequences did not differ systematically. In vivo results were comparable with in vitro results. Regarding susceptibility artifacts and acquisition time, MSVAT-SPACE-STIR might be advantageous over SPACE-STIR for high-resolution and isotropic head and neck imaging. Only for materials with high-susceptibility differences to soft tissue, the use of SEMAC-STIR might be beneficial. Within limited acquisition times, SEMAC-STIR cannot exploit its full advantage over TSE-STIR regarding artifact suppression.

Protocol for the Evaluation of MRI Artifacts Caused by Metal Implants to Assess the Suitability of Implants and the Vulnerability of Pulse Sequences.

As the number of magnetic resonance imaging (MRI) scanners and patients with medical implants is constantly growing, radiologists increasingly encounter metallic implant-related artifacts in MRI, resulting in reduced image quality. Therefore, the MRI suitability of implants in terms of artifact volume, as well as the development of pulse sequences to reduce image artifacts, are becoming more and more important. Here, we present a comprehensive protocol which allows for a standardized evaluation of the artifact volume of implants on MRI. Furthermore, this protocol can be used to analyze the vulnerability of different pulse sequences to artifacts. The proposed protocol can be applied to T1- and T2-weighted images with or without fat-suppression and all passive implants. Furthermore, the procedure enables the separate and three-dimensional identification of signal loss and pile-up artifacts. As previous investigations differed greatly in evaluation methods, the comparability of their results was limited. Thus, standardized measurements of MRI artifact volumes are necessary to provide better comparability. This may improve the development of the MRI suitability of implants and better pulse sequences to finally improve patient care.

Zirconia-Polyurethane Aneurysm Clip

Susceptibility artifacts from metal clips in magnetic resonance (MR) imaging present an obstacle to evaluating the status of clipped aneurysms, parent arteries, and adjacent brain parenchyma. We aimed to develop MR-compatible aneurysm clips. Considering the mechanical and biologic properties, as well as MR compatibility of candidate materials, a prototype clip with a zirconia body and a polyurethane head spring (zirconia clip [ZC], straight, 9-mm long) was developed. The closing forces, opening width of blades, and invitro and invivo artifact volumes in 3 tesla MR imaging were compared among the prototype and commercial metal clips such as a Yasargil clip (YC, curved type, 8.3-mm long) and a Sugita clip (SC, straight type, 10-mm long). An invivo animal study was performed with a canine venous pouch aneurysm model. The closing forces (N) at 1 mm and 8 mm from the blade tip were 2.09 and 3.77 in YC, 1.85 and 3.04 in SC, and 2.05 and 4.60 in ZC. The maximum opening widths (mm) was 6.8, 9.0, and 3.0 in YC, SC, and ZC, respectively. The invitro artifact volumes of YC, SC, and ZC in time-of-flight MR imaging were 26.9, 29.7, and 1.9 times larger than the respective real volumes. The invivo artifact volumes of YC, SC, and ZC were respectively 21.4, 29.4, and 2.6 times larger than real ones. ZC showed the smallest susceptibility artifacts and satisfactory closing forces. However, the narrow opening width of the blades was a weak point.

Dosimetric Impact of Metal Artifacts From Dental Implants and Clinical Implications for Head And Neck IMRT Treatment Planning

Dental implants are increasingly prevalent in the head and neck cancer patient population and result in the creation of artifacts on CT imaging for treatment planning. In our practice, we have noticed more mucosal toxicity adjacent to dental implants and hypothesized that this observation may be due to errors in dose calculation. The purpose of this study was to retrospectively evaluate dosimetric differences in target coverage and organ at risk (OAR) sparing when adjusting for spurious CT measurements attributed to dental metal artifact. Nine patients with dental implants who were previously treated at our institution with definitive radiation for oropharyngeal cancer were selected for this retrospective study. All patients were treated with 6 MV photons using intensity modulated radiation therapy (IMRT). Dose calculation was performed using an algorithm with heterogeneity corrections. Dental implant and streak artifact volumes were contoured and new IMRT plans were generated with identical beam geometry and monitor units using the uncorrected reference CT data set and a corrected CT data set. Artifacts were assigned a soft tissue electron density value with a Hounsfield unit (HU) of zero. Using descriptive statistics, target volumes and OAR dosimetry were reported and compared between the clinical treatment plans and re-calculated plans. Target volumes analyzed were GTV (D95, D98, D99), intermediate-risk PTV (D95, D98, D99), and high-risk PTV (D95, D98, D99, D2cc). The maximum dose, Dmax, was also collected for each plan. OARs analyzed included the bilateral parotids (mean), oral uninvolved (mean), OAR pharynx (mean), mandible (max), and cord (max). The median artifact volume was 41.6 cc (range, 22.5 to 56.8 cc). When accounting for artifact error, there were small but statistically significant relative increases in Dmax (0.24%, P=.0273), mean oral uninvolved dose (0.24%, P=.0234), and mean left parotid dose (0.20%, P=.0469). On average, the hot spot (Dmax) increased by 181 cGy when accounting for artifact. There were no significant dosimetric differences between plans in terms of GTV, intermediate-risk PTV, and high-risk PTV coverage. There were no significant differences for the mandible max dose, cord max dose, OAR pharynx mean dose, or the right parotid mean dose. In this retrospective study, there was minimal dose variation to target volumes and OAR structures when substituting artifact with soft tissue density HUs. There were significant differences in terms of maximum dose and dose to the uninvolved oral cavity, which suggests that ignoring artifacts in CT images during planning may result in greater hot spots. While small, these differences are worthy of further study as they may at least partially contribute to increased rates of empirically observed mucosal toxicity in the vicinity of dental artifacts.